I was going over the grounds in my car, and realized that the firewall-bellhousing ground is missing. Does this connect anywhere on the firewall to anywhere on the bellhousing, or does it matter where it goes? What gauge wire should I use? 12?

Also, I was reading about exhaust grounds, and my car doesn't have any. Are they necessary, and if so, where should they be connected? It sounds like they help ground the O2 sensor, and mine seems to be giving some erratic readings.

 

The firewall to trans ground connects just off to the center of the firewall towards the pass side. I'd use a 8 - 10 gauge wire for it. You can also ground the UIM to the strut tower using the same gauge wire as well...along side the trans ground of course.